Reference image display method for ultrasonography and ultrasonic diagnosis apparatus

ABSTRACT

An ultrasonic image is captured by an ultrasonic probe. A reference image is obtained by extracting a tomographic image corresponding to the scan plane of the ultrasonic image from volume image data that is pre-obtained by a diagnostic imaging apparatus and that is stored in a volume-data storing unit. The ultrasonic image and the reference image are displayed on the same screen. In this case, of the reference image, a portion corresponding to the view area of the ultrasonic image is extracted and the resulting reference image having the same region as the ultrasonic image is displayed as a fan-shaped image.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a Continuation of U.S. application Ser. No.10/556,032, filed Nov. 8, 2005, now U.S. Pat. No. 8,226,560 which is aNational Stage Entry of PCT/JP04/006238, filed May 10, 2004, whichclaims priority from Japanese Patent Application Nos. JP 2003-130490 andJP 2003-130600, both filed on May 8, 2003, the contents of which arehereby incorporated by reference into this application.

TECHNICAL FIELD

The present invention relates to reference-image display methods forultrasonography and ultrasonic diagnosis apparatuses using the methods.More specifically, the present invention relates to a technologypreferably used for reconstructing, using multi-slice-image data of apatient obtained by a diagnostic imaging apparatus, a reference image ofthe same cross section as an ultrasonic scan plane in real time and fordisplaying the reference image and an ultrasonic image on the samescreen. Examples of the diagnostic imaging apparatus include anultrasonic diagnosis apparatus, a magnetic resonance imaging (MRI)apparatus, and an X-ray computed tomography (X-ray CT) apparatus.

BACKGROUND ART

Ultrasonic diagnosis apparatuses, which are one type of diagnosticimaging apparatuses, are frequently used for diagnosis, since they areeasy to handle and are capable of performing noninvasive observation ofarbitrary cross sections in real time. On the other hand, ultrasonicimages captured by the ultrasonic diagnosis apparatuses are generallyinferior in image quality to tomographic images captured by X-ray CTapparatuses or the like. Thus, comprehensive diagnosis may be performedwhile performing comparison with a tomographic image captured by anotherdiagnostic imaging apparatus, such as an X-ray CT apparatus or an MRIapparatus (the tomographic image will hereinafter be referred to as a“reference image”). For example, when hepatophyma or the like is treatedby radiofrequency ablation under the guidance of an ultrasonic image, itis conceived that a treatment portion is pre-located by CT diagnosis anda CT image thereof is used as a reference image to perform the guidancewith the ultrasonic image.

However, when a CT image or MR image is merely rendered as the referenceimage to recognize an association relationship between the images is agreat burden on the operator. This is because the reference imageprovided by a CT image or MR image is typically a tomographic image of across section perpendicular to a body axis, whereas the ultrasonic imageis a tomographic image of an arbitrary cross section specified by theoperator.

Non-patent Document 1 describes an approach to facilitate therecognition of an association relationship between a reference image andan ultrasonic image. In the approach, a position sensor is attached toan ultrasonic probe to determine an ultrasonic scan plane and areference image of the same cross section as the ultrasonic scan planeis reconstructed from multi-slice image data (hereinafter referred to as“volume image data”) of a CT image or MR image and is rendered on adisplay screen. Similarly, Patent Document 1 also proposes a technologyin which a reference image of the same cross section as an ultrasonicscan plane is reconstructed from the volume image data of a CT image orMR image and the reference image and an ultrasonic image are rendered ona display screen in an aligned or superimposed manner or in analternately switched manner.

Patent Document 2 proposes a technology to aid manipulation forintroducing a puncture needle into a body. That is, an ultrasonic scanplane is controlled so as to include the puncture needle and a referenceimage corresponding to the ultrasonic scan plane is cut out and isdisplayed. In the technology, two markers are attached to a body surfaceat a position corresponding to a patient's diseased area, into which thepuncture needle is to be inserted, to obtain the volume image data of areference image. Further, an ultrasonic probe is provided with anintroducing portion for the puncture needle, so that the position andthe angle of the puncture needle relative to the probe is fixed, and asensor for detecting the position and the angle of the probe is attachedto the probe to determine the ultrasonic scan plane. In this manner, acoordinate system for the volume image data and a coordinate system forthe ultrasonic scan plane are associated with each other and a referenceimage corresponding to the ultrasonic scan plane is cut out and isdisplayed.

-   -   Non-patent Document 1: “Radiology” RNSA issued in 1996, page        517, K. Oshio    -   Patent Document 1: Japanese Unexamined Patent Application        Publication No. 10-151131    -   Patent Document 2: Japanese Unexamined Patent Application        Publication No. 2002-112998

DISCLOSURE OF INVENTION

However, in the prior art, although a reference image of a cross sectioncorresponding to the scan plane of an ultrasonic image is cut out and isdisplayed on the same screen, no consideration is given to a scheme formatching display regions and the magnifications of a reference image andan ultrasonic image and. For example, an ultrasonic image is afan-shaped image obtained by capturing one part of a living body of apatient, whereas a CT image or MR image is typically a circular imageobtained by capturing the entire body of the patient. Thus, when thereference image and the ultrasonic image are merely displayed in analigned manner, there is also a problem in that it is difficult torecognize an association relationship of portions he or she desires toobserve.

In addition, in order to obtain an ultrasonic image of a regionincluding a target (e.g., a diseased area) arbitrary specified on areference image by the operator, he or she must manipulate theultrasonic probe to search the region including the target. However, inthe prior art, there is a problem in that no consideration is given to ascheme for facilitating the recognition of the positional relationshipbetween the current ultrasonic scan plane and the target.

Accordingly, a first object of the present invention is to facilitatethe recognition of an association relationship between an ultrasonicimage and a reference image which are displayed on the same screen, thereference image being obtained by another diagnosis apparatus.

A second object of the present invention is to facilitate therecognition of the positional relationship between a target specified onan arbitrary reference image by an operator and the current ultrasonicscan plane.

In order to achieve the first object, an ultrasonic diagnosis apparatusof the present invention includes ultrasonic image generating means forreconstructing an ultrasonic image from reflection echo signals outputfrom an ultrasonic probe, storing means for storing volume image datapre-obtained by a diagnostic imaging apparatus; reference-imagegenerating means for extracting tomographic image data corresponding toa scan plane of the ultrasonic wave from the volume image data stored inthe storing means and reconstructing a reference image, controllingmeans for causing the reference image and the ultrasonic image to bedisplayed on a screen, and displaying means for displaying the referenceimage and the ultrasonic image. In accordance with the tomographic imagedata and a positional relationship between the ultrasonic probe and apatient, the reference-image generating means extracts tomographic imagedata of a portion corresponding to a view area of the ultrasonic imageto generate the reference image.

Thus, according to the present invention, since the reference image ofthe same region corresponding to the fan-shaped view-area of theultrasonic image is displayed as a fan-shaped image, it is possible toeasily recognize an association relationship between both the images. Inthis case, it is preferable that, of the reference image, the regioncorresponding to the view area be displayed with the same magnificationas the ultrasonic image, since the recognition of an associationrelationship between both the images is further facilitated. It is alsopreferable that, of the reference image, brightness of a portion out ofthe view area of the ultrasonic image be reduced to perform display.With this arrangement, it is possible to perform comparison andobservation without losing information of the reference image.

Further, displaying an acoustic shadow of the ultrasonic image on thereference image in a simulated manner further facilitates therecognition of an association relationship between both the images.Also, the ultrasonic image and the reference image can be displayed onthe screen in an aligned manner, but the configuration is not limitedthereto. A composite image of the ultrasonic image and the referenceimage can be displayed on the screen. The composite image can be animage obtained by superimposing a transparent image of the referenceimage on the ultrasonic image. Also, the composite image can be adifference image between the reference image and the ultrasonic image.

It is preferable that the reference-image generating means change animage size of the reference image in accordance with a speed of movementof the ultrasonic probe. This makes it possible to display the referenceimage according to a quick movement of the ultrasonic image, thusenhancing the freedom of manipulating the probe during the comparisonand observation.

In order to achieve the second object, the ultrasonic diagnosisapparatus of the present invention includes a 3D body-mark determiningunit for determining a positional relationship between the scan planeand a target set in the volume image data to cause a direction and adistance of the target relative to the scan plane to be displayed on thescreen.

Additionally, the ultrasonic diagnosis apparatus of the presentinvention may further includes a cine-memory for storing the ultrasonicimage reconstructed by the ultrasonic-image generating means, a positionsensor for detecting a position and an inclination of the ultrasonicprobe, scan-plane-coordinate determining means for determiningscan-plane coordinates of the ultrasonic image in accordance with anoutput from the position sensor, and scan-plane-coordinate-systemstoring means for storing the determined scan-plane coordinates. Thereference-image generating means reads the scan-plane coordinates of theultrasonic image from the scan-plane-coordinate-system storing means,reads the tomographic-image data corresponding to the read scan-planecoordinates, and reconstructs the reference image. The image processingmeans reads the ultrasonic image from the cine-memory and causes thereference image corresponding to the read ultrasonic image, thereference image being output from the reference-image generating means,to be displayed. With this arrangement, since ultrasonic images aresequentially read from the cine-memory and displayed and referenceimages corresponding to the ultrasonic images are sequentially cut outand displayed, comparison and observation can be performed using movingimages.

It is also preferable that the ultrasonic diagnosis further includes atleast one of a posture sensor for detecting a change in the posture ofthe patient and a sensor for detecting breathing and further hascorrecting means for correcting the scan-plane coordinates in accordancewith an amount of internal-organ movement caused by a posture change orthe breathing of the patient during ultrasonic diagnosis. With thisarrangement, a displacement between the reference-image coordinatesystem and the ultrasonic-image coordinate system, the displacementbeing resulting from internal-organ movement caused by the breathing ora posture change of the patient, can be corrected. Thus, the accuracy ofcomparison and observation of both the images can be improved.

In addition or instead, the configuration can be such that, after thescan plane of the ultrasonic probe is scanned and one of an ultrasonicimage and a reference image which has a distinctive point is searchedfor and frozen, the ultrasonic probe is manipulated, an image that isother than the frozen ultrasonic image or reference image and thatmatches the frozen one of the images is displayed and frozen, and acoordinate difference between scan-plane coordinates for the frozen oneof the images and the other image is determined, so that the scan planecoordinates can be corrected based on the determined coordinatedifference.

Further, in addition to the above-described configuration, theultrasonic diagnosis apparatus can include: a position sensor fordetecting a position and an inclination of the ultrasonic probe inassociation with a reference coordinate system; scan-plane-coordinatedetermining means, for determining scan-plane coordinates of anultrasonic image captured by the ultrasonic probe in association withthe reference coordinate system, in accordance with an output from theposition sensor; reference-point inputting means for setting a referencepoint on a reference image displayed on the screen based on the volumeimage data obtained in association with the reference coordinate system;volume-data-coordinate determining means for determining coordinates, oftomographic data of the volume image data associated with the scan-planecoordinates, by determining a coordinate relationship between theposition of the ultrasonic probe and a region that corresponds to thereference point and that exists on an ultrasonic image obtained bybringing the ultrasonic probe in contact with a body surface of thepatient; and volume-data-coordinate storing means for storing thetomographic-image-data coordinates determined by thevolume-data-coordinate determining means. The reference-imagereconstructing means can read the coordinates of the tomographic imagedata, associated with the scan-plane coordinates determined by thescan-plane-coordinate determining means, from the volume-data-coordinatestoring means and can extract the reference image. With thisarrangement, the reference point for aligning the coordinate systems canbe set inside the body of the patient. Thus, compared to the prior artin which a reference point is set on the body surface, the freedom ofsetting the reference point is increased and thus the accuracy ofcomparison and observation can be further improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a basic diagnostic imaging system to whichan ultrasonic diagnosis apparatus of one embodiment of the presentinvention is applied.

FIG. 2 is a block diagram of a specific diagnostic imaging system towhich an ultrasonic diagnosis apparatus of another embodiment of thepresent invention is applied.

FIG. 3 is a flow chart showing a sequence of a drawing procedure for anultrasonic image and a reference image in one embodiment of the presentinvention.

FIG. 4 is a view showing a display example of an ultrasonic image, areference image, a composite image, and a 3D body mark according to afeature of the present invention.

FIG. 5 is a view showing a display example of an ultrasonic image, areference image, a composite image, and a 3D body mark which arepreferable for navigation according to a feature of the presentinvention.

FIG. 6 is a block diagram of a specific diagnostic imaging system towhich an ultrasonic diagnosis apparatus of still another embodiment ofthe present invention is applied.

FIG. 7 are block diagrams of a position-sensor equipped probe in oneembodiment according to the present invention.

FIG. 8 show the configuration and the processing procedure ofbreathing-amount determining means according to the present invention.

FIG. 9 is a detailed block diagram of a scan-plane-coordinatedetermining unit and a scan-plane-coordinate storing unit in theembodiment shown in FIG. 2.

FIG. 10 is a flow chart of initialization processing for coordinateassociating processing in the embodiment shown in FIG. 6.

FIG. 11 is a flow chart of embodiment of a reference-image displayprocessing, during ultrasonic diagnosis, in the embodiment shown in FIG.6.

FIG. 12 are diagrams illustrating an association relationship betweenvolume image data and a scan-plane coordinate system.

FIG. 13 is a flow chart of one embodiment for correcting areference-coordinate-system displacement caused by breathing or the likeof a patient.

FIG. 14 shows one example of a coordinate adjustment screen forassisting processing for correcting scan plane coordinates.

FIG. 15 is a view illustrating a method for correcting acoordinate-system displacement resulting from internal-organ movementcaused by the breathing of the patient.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will be described belowwith reference to the accompanying drawings.

First Embodiment

FIG. 1 is block diagram of a basic diagnostic imaging system to which anultrasonic diagnosis apparatus of one embodiment of the presentinvention is applied. As shown, the diagnostic imaging system includesan ultrasonic diagnosis apparatus 101 according to one embodiment of thepresent invention and a medical diagnostic imaging apparatus 102 forobtaining volume image data that provides as a reference image. Thevolume image data refers to the data of multi-slice images obtained bycapturing the inside of the body of a patient along multiple sliceplanes. The data of the volume images captured by the medical diagnosticimaging apparatus 102 is input to the ultrasonic diagnosis apparatus101. A computed tomography apparatus (X-ray CT apparatus) or a magneticresonance imaging apparatus (MRI apparatus) can be used as the medicaldiagnostic imaging apparatus 102. CT images and MR images have higherimage qualities than ultrasonic images, as is known, and thus aresuitable as reference images for ultrasonic images, which are inferiorin image quality. However, when a temporal change in tissues of apatient is diagnosed with ultrasonic waves, the volume image data of apre-obtained ultrasonic image can be drawn as the reference image.

In FIG. 1, descriptions of functions commonly included in the ultrasonicdiagnosis apparatus 101 are omitted to avoid complexity, and only thefunctions of major units associated with displaying the reference imageaccording to a feature of the present invention are described. As shown,the ultrasonic diagnosis apparatus 101 can broadly be divided into asection for reconstructing an ultrasonic image and a section forreconstructing the reference image. The former ultrasonic-imagereconstructing section has a probe 104 and an ultrasonic-imagedetermining unit 105. The latter reference-image reconstructing sectionhas a volume-data storing unit 107 and a reference-image determiningunit 111.

The ultrasonic-image determining unit 105 provides ultrasonic-imagegenerating means for reconstructing an ultrasonic image in accordancewith a reflection echo signal output from the probe 104. Theultrasonic-image determining unit 105 is adapted to associate signalsoutput from a position sensor 108 with the reconstructed ultrasonicimage. On the other hand, a controlling unit 120 is adapted to determinethe scan-plane coordinates of the probe 104 in accordance with signalsoutput from the position sensor 108 and to output the determinedscan-plane coordinates to the reference-image determining unit 111. Thereference-image determining unit 111 provides a reference-imagegenerating means for extracting tomographic image data, corresponding tothe scan-plane coordinates input from the controlling unit 120, from thevolume-data storing unit 107 and reconstructing the reference image.Thus, the ultrasonic image reconstructed by the ultrasonic-imagedetermining unit 105 and the reference image reconstructed by thereference image determining unit 111 are adapted to be displayed on amonitor 114.

In particular, the reference-image determining unit 111 is configuredsuch that it extracts tomographic-image data-of a region correspondingto the view area of an ultrasonic image, in accordance with thescan-plane coordinates that are input from the controlling unit 120 andthat are based on the positional relationship between the probe 114 andthe patient, and generates a reference image.

According to the present embodiment configured as described above andshown in FIG. 1, a reference image corresponding to the fan-shaped viewarea of an ultrasonic image, the reference image and the ultrasonicimage captured from the same region, is displayed as a fan-shaped image.This makes it possible to easily recognize an association relationshipbetween both the images. In this case, displaying, of the referenceimage, a region corresponding to the view area of the ultrasonic imagewith the same magnification as the ultrasonic image can furtherfacilitate the recognition of an association relationship between boththe images. Also, displaying, of the reference image, a region that isout of the view area of the ultrasonic image, with reduced brightness,allows comparison and observation without loosing the information of thereference image.

Second Embodiment

FIG. 2 shows the configuration of a specific diagnostic imaging systemto which an ultrasonic diagnosis apparatus of the present invention isapplied. In the figure, means having the same functional configurationsas those in FIG. 1 are denoted with the same reference numerals and thedescriptions thereof are omitted. In FIG. 2, a scan-plane-coordinatedetermining unit 109 and a scan-plane-coordinate storing unit 110correspond to the configuration of the major unit of the controllingunit 120. A cine-memory 106 stores an ultrasonic image reconstructed bythe ultrasonic-image determining unit 105. A 3D body-mark determiningunit 112 is provided in connection with the reference-image determiningunit 111. An adder 113 is configured as image processing means forappropriately combining images generated by the cine-memory 106, thereference-image determining unit 111, and the 3D body-mark determiningunit 112. The monitor 114 is adapted to display images generated by thecine-memory 106, the reference-image determining unit 111, and the 3Dbody-mark determining unit 112 and the image processed by the adder 113.

The probe 104 transmits/receives ultrasonic waves to/from a patient 103and has built-in multiple transducers that generate ultrasonic waves andthat receive reflection echoes. The ultrasonic-image determining unit105 receives reflection echo signals output from the probe 104 andconverts the received signals into digital signals to create anultrasonic image 302, such as a tomographic image (B-mode image) or acolor flow mapping image (CFM image), of a diagnosis region, as shown inFIG. 3 and so on. The cine memory 106 receives ultrasonic images createdby the ultrasonic-image determining unit 105 and stores ultrasonicimages for multiple frames.

The volume-data storing unit 107 receives the volume image data of areference image, captured by the medical diagnostic imaging apparatus102, through a network or via a portable storage (MO) medium, such as amagneto-optical disk, and stores the volume image data in the ultrasonicdiagnosis apparatus 101.

The position sensor 108 is attached to the probe 104 to detect thethree-dimensional position and inclination of the probe. A source 116for a coordinate system including the patient 103 is placed in thevicinity of a bed 115 on which the patient 103 lies. The principle ofdetecting the three-dimensional position and inclination of the probe104 is that magnetic signals generated in a three-dimensional space bythe source 116 is detected by the position sensor 108 and thethree-dimensional position and inclination in a reference coordinatesystem formed by the source 116 are detected. A position sensor systemconstituted by the position sensor 108 and the source 116, is not onlylimited to a magnet-based system but also may employ, for example, aknown position sensor system, such as a system utilizing light.

In accordance with signals output from the position sensor 108 and thesource 116, the scan-plane-coordinate determining unit 109 obtains theposition and inclination information of the probe 104 in the referencecoordinate system to determine scan-plane coordinates including theposition and the inclination of a ultrasonic scan plane relative to thepatient 103. The scan-plane-coordinate determining unit 109 is alsoadapted to calculate scan-plane coordinates in a reference-imagecoordinate system, in accordance with the determined scan-planecoordinates. That is, the scan-plane-coordinate determining unit 109 isadapted to determine scan-plane coordinate data including, for example,x, y, and z coordinate data of one corner of a scan plane and rotationangles about x, y, and y axes of the scan plane in a volume-image-datacoordinate system. The scan-plane-coordinate data determined by thescan-plane-coordinate determining unit 109 is input to thescan-plane-coordinate storing unit 110 and scan plane coordinates formultiple frames are stored therein. In this case, it is preferable thatthe number of frames for scan plane coordinates stored be substantiallythe same as the number of frames of ultrasonic images captured in realtime and stored in the cine-memory 106. The reference-image determiningunit 111 provides reference-image reconstructing means, and receivesscan-plane coordinate data and reconstructs a reference image of thesame cross section as an ultrasonic scan image.

Next, a detailed configuration of the ultrasonic diagnosis apparatus 101according to the present embodiment will be described in conjunctionwith the operation thereof. FIG. 3 is a flow chart for rendering anultrasonic image and a reference image of the same cross section. Thedrawing processing is broadly classified into an ultrasonic-imageprocessing sequence 201 for rendering an ultrasonic image and storingthe scan-plane coordinates in a storage unit and a reference-imageprocessing sequence 202. These two sequences 201 and 202 are executed insuch a manner that starts and freezes are synchronized.

First, when an operator starts the two sequences 201 and 202, adetermination is made as to whether a freeze instruction is input (51).When freeze is not performed, the ultrasonic-image processing sequence201 drives the probe 104 to transmit/receive ultrasonic waves to/fromthe patient 103 (S2). The ultrasonic-image determining unit 105reconstructs an ultrasonic image in accordance with the reflection echosignals output from the probe 104 (S3). The reconstructed ultrasonicimage is stored in the cine-memory 106 (S4) and is drawn on the monitor114 (55).

At this point, the position sensor 108 obtains the position andinclination of the probe 104 in synchronization with thetransmission/reception of the ultrasonic waves (S12). In accordance withthe position and inclination information input from the position sensor108, the scan-plane-coordinate determining unit 109 determinesscan-plane coordinates (S13). The determined scan-plane coordinates aresequentially written to the scan-plane-coordinate storing unit 110(S14). In this case’, the processing of steps 51 to 55 in theultrasonic-image processing sequence 201 and the processing of steps S12to S14 are executed in synchronization with each other.

On the other hand, in the reference-image processing sequence 202, adetermination about freezing is made (S21). When freezing is notperformed, scan-plane coordinates are read from thescan-plane-coordinate storing unit 110 (S22). Based on volume imagedata, the reference-image determining unit 111 reconstructs a referenceimage of the same cross section as the ultrasonic image (S25). Thereconstructed reference image is drawn on the monitor 114 (S26). Theprocessing of steps 523 and 524 will be described below.

Next, when the operator inputs an instruction for freezing theprocessing, the ultrasonic-image processing sequence 201 and thereference-image processing sequence 202 are adapted to execute cineplaybacks in S31 and S32, respectively, based on the determination insteps Si and S21. The cine playback of an ultrasonic image is executedby referring to the ultrasonic image data stored in the cine memory 106.In contrast, the cine playback of a reference image is executed by usingthe scan-plane coordinate data stored in the scan-plane-coordinatestoring unit 110 and by reconstructing a reference image correspondingto the scan plane based on the volume image data. The ultrasonic imagedata stored in the cine-memory 106 and the scan-plane coordinate datastored in the scan-plane-coordinate storing unit 110 are stored insynchronization with each other, it is possible to render an ultrasonicimage and a reference image whose time phases are the same. The cineplayback of an ultrasonic image is performed by referring to theultrasonic-image data stored in the cine-memory 106, whereas thecine-playback of a reference image is performed by referring to thescan-plane-coordinate data stored in the scan-plane-coordinate storingunit 110. Thus, it is sufficient for the memory of thescan-plane-coordinate storing unit 110 to store onlyscan-plane-coordinate data, the memory capacity can be reduced.Similarly, for storing a moving image, merely storing scan-planecoordinates corresponding to volume image data makes it possible to playback the moving picture while reconstructing it from the volume imagedata. Thus, a moving-image file having a small file size can be created.

Now, an image-display processing method according to a feature of thepresent invention will be described with reference to FIG. 4. First, inaccordance with the enlargement factor (magnification) of the ultrasonicimage 302, the reference-image determining unit 111 enlarges or reducesa reference image and displays it at the same magnification, as shown ina reference image 301 Shown in FIG. 4. The reference-image determiningunit 111 also extracts an out-of-view area 312 corresponding to afan-shaped viewing angle 311 of the ultrasonic image 302 and reduces thebrightness of a reference image corresponding to the region 312. As aresult, the reference image is displayed in the same display format andwith the same magnification as those of the ultrasonic image 302, thusmaking it easy to recognize an association relationship between theultrasonic image 302 and the reference image. This arrangement alsomakes it possible to perform display without losing the information of areference image in the out-of-view area of the ultrasonic image. Also,an acoustic shadow 307, such as a bone 313 (or air), appears on theultrasonic image 302. It is preferable that a region corresponding tothe acoustic shadow 307 be extracted based on determination, forexample, using CT values of a CT image; and the brightness of an area308 that is deeper than that region be reduced. Similarly, an area 310is extracted, using CT values, from a region where a blood vessel existsand the region is displayed, for example, in red, like an ultrasonic CFM(color flow mapping) image 309. This makes it possible to display thereference image 301, which allows easy comparison with the ultrasonicimage 302.

On the other hand, the 3D body-mark determining unit 112 extracts athree-dimension visualized image, such as a 3D body mark 304 in FIG. 4,by using volume image data, superimposes a scan plane 314 in atranslucent color on the three-dimension visualized image, and displaysthe resulting image. As the three-dimensional visualized image, forexample, a known method, such as volume rendering or surface rendering,can be used. Displaying the 3D body mark 304 allows the positionalrelationship between the patient 103 and the scan plane 314 to berecognized in three dimensions. The 3D body-mark determining unit 112may be provided with a function for extracting a region of interest,specified by the operator, from the volume image data and determiningthe distance and the direction from the scan plane to the region ofinterest.

The adder 113, which provides the image processing means, is intended todetermine a composite image 303 of the reference image 301 and theultrasonic image 302. The adder 113, for example, converts the referenceimage 301 into a translucent-color image and superimposes it on theultrasonic image 302. Instead, a difference image between the referenceimage 301 and the ultrasonic image 302 may be obtained and drawn. Thiscan facilitate that the reference image 301 and the ultrasonic image 302are compared with each other using one image. With the difference image,for example, when an ultrasonic volume image data obtained in advance isused as the reference image, it is useful to diagnose a temporal changein living-body tissues of the patient.

Thus, as shown in FIG. 4, the ultrasonic ‘image 302, the reference image301, the composite image 303, and the 3D body-mark 304 of the same crosssection are drawn on the monitor 114. This allows the operator toperform effective diagnosis while comparing those images.

For example, using the medical diagnostic imaging apparatus 102 toobtain volume image data centering at a treatment region before medicaltreatment, causing the ultrasonic diagnosis apparatus 101 to capture animage of the treatment region after the medical treatment, anddisplaying a reference image before the medical treatment and anultrasonic image after the medical treatment, for example, in an alignedmanner can facilitate determination of the effect of the medicaltreatment. Also, synthesizing an image of a difference between thereference image before the medical treatment and the ultrasonic imageafter the medical treatment and displaying the difference image furtherfacilitates the determination of the effect of the medical treatment. Inparticular, performing display in added color according to the degree ofthe difference can further facilitate viewing.

By reducing the image size and changing the frame rate, thereference-image determining unit 111 can increase the speed ofreconstructing a reference image in accordance with the motion of theprobe 104. That is, the reference-image determining unit 111 determinesthe movement speed and the rotation speed of the scan plane, based onthe scan-plane coordinate data. When the speed is greater than a certainthreshold, the reference-image determining unit 111 reduces the imagesize to reconstruct the reference image at a high speed. That is, whenthe movement of the probe 104 is fast, priority is given to the framerate over the image quality to draw the reference image at a high speed,and when the movement of the probe 104 is slow, priority is given to theimage quality over the frame rate to reconstruct and draw the referenceimage. This makes it possible to draw the reference image so as tocorrespond to the ultrasonic image that varies according to the motionof the probe 104.

An image-display processing method with a navigation function willfurther be described with reference to FIG. 5. This ultrasonic diagnosisapparatus is adapted to allow navigation for guiding the scan plane ofthe probe 104 to a target 405 that the operator pre-set on a referenceimage in the volume image data. The target 405 can be set by designatinga region with a mouse, for example, on an axial image, sagittal image,coronal image, and three-dimensional visualized image. The 3D body-markdetermining unit 112 calculates the distance and direction from thecurrent scan plane to the center of the target 405 and displays athree-dimensional arrow image and numeric values in a display region 407on the screen of a 3D body mark 404. The boundary of the region of thetarget 405 is also rendered in a reference image 401 and an ultrasonicimage 402. This allows the operator to visually recognize the distancefrom the current ultrasonic scan plane 314 to the target 405. When thetarget 405 enters the scan plane 314, a boundary determined from thereference image 401 is also displayed in the ultrasonic image 402.Consequently, it is easy to recognize an association relationshipbetween the reference image 401 and the ultrasonic image 402.

Additionally, a region of interest (ROI) 406 that the operator set onany of the ultrasonic image 402, the’ reference image 401, and acomposite image 403 is displayed on all the images. This facilitates therecognition of an association relationship of the region of interest.

Third Embodiment

FIG. 6 shows the configuration of a diagnostic imaging system to whichan ultrasonic diagnosis apparatus of another embodiment of the presentinvention is applied. In FIG. 6, what are different from the embodimentshown in FIG. 2 are that a breathing sensor 117 for detecting the amountof breathing of the patient 103 and a posture sensor 118 for detectingthe body movement are provided and outputs of the detections are inputto the scan-plane-coordinate determining unit 109. Although processingfor associating a volume-image-data coordinate system with a scan-planecoordinate system was omitted in the embodiment in FIG. 2, detailsthereof will be described.

In the present embodiment, as shown in FIG. 7A, the position sensor 108is attached to one surface of the probe 104 to make it possible todetect the position and inclination of the probe 104, i.e., the positionand inclination of the ultrasonic scan plane, in a coordinate systemformed by the source 116. In FIG. 7A, transducers are arranged on acircular arc surface of the probe 104 and the distance between a centerpoint 201 of the transducers and a center point 202 of the positionsensor 108 has been accurately determined. The relationship between theprobe 104 and the position sensor 108 is not limited to what is shown inthe figure and can be configured as shown in FIG. 7B. That is, thearrangement can be such that a bar-shaped pointer 203 is detachablyattached in association with the position sensor 108 and an end point204 of the pointer 203 is used as a reference point relative to thecenter point 202. With this arrangement, the probe 104 of the presentembodiment can also be utilized as a pointing device.

In the same manner as the position sensor 108, the posture sensor 118 isattached to the body surface of the patient 103 so as to measure theposition and inclination of the patient 103 in the reference coordinatesystem formed by the source 116. The breathing sensor 117 measures theamount of breathing of the patient 103. For example, as shown in FIG.8A, the breathing sensor 117 having a function similar to the positionsensor 108 is attached to the body surface of the patient 103, lying onthe bed 115, so as to detect the amount of body-surface movement causedby the breathing. As shown in FIG. 8B, the measured amount of movementcan be converted into an amount of breathing.

While the scan-plane-coordinate determining unit 109 and thescan-plane-coordinate storing unit 110 are configured to be essentiallythe same as those in the second embodiment, features and functionsaccording to the present embodiment will be specifically described. Thescan-plane coordinate determining unit 109 has a function for correctingscan-plane coordinates in accordance with the posture information of thepatient 103 and the amount of breathing of the patient 103. Thescan-plane coordinates as used herein refer to the coordinates of anultrasonic scan plane imaged by the probe 104. As shown in FIG. 9, thescan-plane-coordinate determining unit 109 and the scan-plane-coordinatestoring unit 110 include a scan-plane coordinate-system storing unit 211a volume-image-data coordinate-system storing unit 212, aposture-change-amount determining unit 213, aninternal-organ-movement-amount determining unit 214, a correcting unit215, and a corrected-scan-plane-coordinate determining unit 216. As inthe embodiment shown in FIG. 2, the reference-image determining unit 111receives the scan-plane coordinates, extracts same-cross-section imagedata corresponding to the scan-plane coordinates from the volume-datastoring unit 107, and reconstructs a reference image. The adder 113 thendraws a reference image, output from the reference-image determiningunit 111, and an ultrasonic image, read from the cine-memory 106, on themonitor 114. The ultrasonic image and the reference image are typicallydisplayed on the same screen in an aligned manner, but instead, can bedisplayed in a superimposed manner. When they are displayed in asuperimposed manner, it is desired that the reference image betranslucent.

Now, processing for associating volume-image-data coordinates withscan-plane coordinates will be described with reference to FIGS. 10, 11,and 12. The coordinate association processing in the present embodimentcan be broadly classified into an initialization stage shown in FIG. 10and a diagnosis stage shown in FIG. 11.

First, a description is given of the initialization stage shown in FIG.10, i.e., processing during the imaging of volume image data. In stepS101, as shown in FIG. 12B, the x axis of the source 116 for theposition sensor is oriented in the lateral direction of the bed 115, they axis is oriented in the longitudinal direction of the bed 115, and thez axis is oriented in the vertical direction of the bed 115 to therebyplace the source. Thus, the x, y, and z axes of a source coordinatesystem that has the origin at, for example, a center 224 of the source116 are aligned parallel to the x, y, and z axes of a coordinate systemhaving an original 225 at one corner of volume image data shown in FIG.12A. That is, volume data 221 shown in FIG. 12A is obtained by typicallylaying the patient 103 on the bed 115 and capturing a tomographic imageperpendicular to the body axis (the y-axis direction) of the patient103. Placing the source 116 so as to be aligned with the bed 115 allowsthe x, y, and z axes of the reference coordinate system of the source116 and the coordinate system of the volume data 221 to be substantiallyparallel to each other.

Next, in step S102, a reference point 223 is set in the volume data 221.The reference point 223 is set on an operation screen by using apointing device, such as a mouse. The operation screen is displayed witha reference image obtained by’ imaging volume image data. The operationscreen may include an axial image, sagittal image, coronal image, orthree-dimensional visualized image. Designating the reference point 223on any of the images makes it possible to set the reference point 223 onthe body surface or inside the body in the volume image data.

In contrast, in step S103, a reference point 222 in the scan-planecoordinate system is set, for example, by locating the probe 104 withthe position sensor 108 at a position corresponding to the referencepoint 223 of the volume data 221 and holding the probe 104. For example,when the reference point 222 of the volume data is designated on thebody surface, the contact point 201 of the probe 104 is placed at abody-surface position of the actual patient 103, the body-surfaceposition corresponding to the reference point 222, to set the referencepoint 222 in the scan-plane coordinate system. In this case, since theposition of the reference point 222 and the position of the referencepoint 223 match each other, it is possible to match the coordinatesystem of the volume image data and the coordinate system of the scanplane. In this case, the probe 104 is used as a pointing device. Here,in order to facilitate the work of placing the probe at the body-surfaceposition of the actual patient, the body-surface position beingcorresponding to the position of the reference point specified in thevolume image data, it is preferable that a distinctive point (e.g., axiphoid process or a blood vessel branch) that can be easily found onthe body surface from the external view be selected as the referencepoint 223 specified in the volume image data.

On the other hand, when the reference point in the volume image data isspecified inside the body, the probe is manipulated, an ultrasonic imagecontaining a region containing the in-vivo reference image 223 isdisplayed, and a region corresponding to the in-vivo reference point 223is specified on the ultrasonic image by using a pointing device, such asa mouse. Then, the distance between the specified point and the center202 or the contact point 201 of the probe 104 is determined and thecoordinates of the two reference points 222 and 223 are associated witheach other. In this case, in order to easily identify the in-vivoreference point 223 on the ultrasonic image, it is preferable that aneasy-to-find distinctive point on the ultrasonic image be selected asthe reference point specified in the volume image data, as describedabove.

Next, in step S104, relationship data for associating the scan-planecoordinate system with the reference coordinate system of the source 116is determined. First, the origin of the patient 103 in the real space isset at the reference point 222. The coordinate axes of the scan planecoordinate system are set parallel to the coordinate axes of the sourcecoordinate system. Then, the position (X, Y, and Z) of the referencepoint 222 of the probe 104, the position being detected by the positionsensor 108, is determined, the scan-plane coordinate system and thesource coordinate system are associated with each other, and theresulting association data is stored in the scan-plane coordinate-systemstoring unit 211 shown in FIG. 9. In this manner, the volume-image-datacoordinate system and the scan-plane coordinate system can be associatedwith each other via the reference coordinate system of the source 116.In step S105, data for associating the volume-image-data coordinatesystem with the scan-plane coordinate system is created and is stored inthe volume-image-data coordinate-system storing unit 212 shown in FIG.9.

Since the source 116 is placed in step S101 such that the coordinateaxes of the volume-image-data coordinate system are parallel to thecoordinate axes of the source coordinate system. Setting only onereference point 223 in the volume-image-data coordinate system canfacilitate that those two coordinate systems are associated. That is,placing the source 116 in an appropriate direction according to thedirection of the body axis of the patient can readily align thecoordinate systems. However, in the present invention, three referencepoints 223 can also be set. In this case, the accuracy of associatingthe coordinate systems can be improved. For example, when the coordinatesystems are determined with three reference points, one of the threepoints is designated as the origin of the coordinate system, vectorsfrom the origin to the remaining two points are designated as an X axisand a Y axis, and an axis perpendicular to the x and y axes isdesignated as a Z axis to thereby achieve the alignment. This makes itpossible to associate the coordinate systems without caring about thedirection of the placed source 116. The remaining two points can beautomatically set on the screen by causing a measurement tool forperforming measurement on image data to perform the above-describedprocessing.

The association data between the volume-image-data coordinate system andthe scan-plate coordinate system, the association data being created asdescribed above, is used during ultrasonic diagnosis to determinescan-plane coordinates according to a procedure shown in FIG. 11. Thescan-plane-coordinate determining unit 109 determines the scan planecoordinates, in accordance with the position and inclination of theprobe 104 which are detected by the position sensor 108 attached to theprobe 104 (step S106). Next, the reference-image determining unit 111cuts a reference image, corresponding to the scan-plane coordinates, outfrom the volume image data and causes the reference image to bedisplayed on the monitor 114 via the adder 113 (step S107). This allowsthe operator to draw a reference image that matches an ultrasonic imagecorresponding to an arbitrary set position and direction of the probe,thereby improving the accuracy of diagnosis.

Next, a feature and a function of the present embodiment ‘for correctingthe scan plane coordinates in accordance with a change in the postureand so on will be described. That is, as diagnosis proceeds, adisplacement may occur between the coordinate systems of the volumeimage data and the scan plane, due to factors, such as a change in theposture of the patient and internal-organ movement caused by thebreathing of the patient. Such a displacement may make it impossible todraw a reference image that matches the ultrasonic scan plane.Accordingly, in the present embodiment, in a diagnosis stage, the scanplane-coordinate determining unit 109 is adapted to correct adisplacement in the scan-plane coordinate system.

Correction for a change in the posture of the patient will be describedfirst. The posture of the patient can be detected with the posturesensor 118 shown in FIG. 6. Thus, a difference between the postureduring initialization and the posture during diagnosis is determined bythe posture-change-amount determining unit 213, and in accordance withdifference, the scan-plane coordinate system is shifted and rotated toperform correction.

Next, means for correcting a coordinate-system displacement due tointernal-organ movement caused by the breathing of the patient will bedescribed with reference to FIG. 13. The operator performs thiscorrection processing, while viewing a rendered reference image andultrasonic image. The operator first pays attention to the referenceimage. The operator displays, for example, a distinctive cross section,including the patient's blood vessel such as a portal vein or superiormesenteric artery, and performs freezing, while manipulating the probe104 (step S201). Next, the operator pays attention to the ultrasonicimage, and renders the same cross section as the frozen image of thereference image and performs adjustment, while performing visualcomparison with the frozen image (step S202). Here, a difference (theamount of change) between the scan-plane coordinates during the freezingand the scan plane-coordinates during the adjustment corresponds to theamount of internal-organ movement. Thus, the scan-plane coordinatedetermining unit 109 determines a difference (the amount of change)between the scan-plane coordinates during the freezing and thescan-plane coordinates during the adjustment (step S203). The scan-planecoordinate system is shifted and rotated by an amount corresponding tothe difference to thereby perform correction (step S204). Consequently,even when the depth of breathing of the patient differs from that in theinitialization stage, the scan-plane coordinates and thevolume-image-date coordinate system can be correctly associated witheach other.

During the correction processing in FIG. 13, a coordinate adjustmentscreen 231 shown in FIG. 14 is displayed so as to allow a freeze key 232and an adjust key 234 to be operated on the screen. Also, the amount ofmovement and the amount of rotation which are related to the correctioncan also be displayed in parameter edit boxes 232. The operator canperform correction by directly inputting numeric values to the editboxes 232.

In addition, an input amount of breathing is measured by the breathingsensor 117, the correction is repeated at multiple depths of breathing,and the correlation between the amount of breathing and the amount ofinternal-organ movement is determined. With this approach, adisplacement caused by internal-organ movement can be automaticallycorrected in accordance with an input from the breathing sensor.

Hereinabove, a volume-image-data reference image having a distinctivepoint is frozen and an ultrasonic scan plate corresponding to thereference image has been determined. Conversely, the arrangement mayalso be such that an ultrasonic scan plane having a distinctive point isfrozen and image processing is performed to automatically determine areference image corresponding to the ultrasonic scan plane.Specifically, an ultrasonic scan plane displaying a distinctive point ofthe patient is frozen and the ultrasonic scan plane is recorded in astorage medium, such as the cine-memory 106. By using a known patternmatching method, the reference-image determining unit 111 extracts areference image corresponding to the distinctive point of the frozenultrasonic scan plane from the volume image data stored in thevolume-data storing unit 107. The reference image extracted as a resultof matching is displayed on the monitor 114. In the reference-imagematching processing, there is no need to search all the volume imagedata. Thus, only data regarding the scan-plane side, viewed in the scandirection of the ultrasonic probe 104, may be extracted to matchdistinctive regions. Magnification may also be adjusted such that adistinctive point on the ultrasonic scan plane and a distinctive pointon the reference image have the same magnification. In this manner,extracting a reference image from image information having a distinctivepoint can enhance the accuracy of aligning the ultrasonic scan plane andthe reference image.

In addition, another example of the means for correcting acoordinate-system displacement due to internal-organ movement caused bythe breathing of the patient will be described with reference to FIG.15. As in the case of FIG. 13, the operator performs this correctionprocessing while viewing a rendered reference image and an ultrasonicimage. First, the probe 104 is placed on the patient so that crosssections perpendicular to a direction in which the internal organs movedue to breathing are displayed. The direction in which the internalorgans move due to breathing is typically the body axis direction of thepatient. The probe 104 placed on the patient is then moved in theinternal-organ movement direction, and distinctive ultrasonictomographic images, including a blood vessel such a portal vein orsuperior mesenteric artery, are rendered. At this point, due to theoccurrence of a displacement between the volume-image-data coordinatesystem and the scan-plate coordinate system, a cross-sectiondisplacement in the body axis direction occurs between the ultrasonicimage and the reference image. In this state, the ultrasonic image andthe reference image are frozen, cine playback is performed, and theoperator specifies a corresponding combination of a reference image andan ultrasonic image. For example, in the example shown in FIG. 15, sinceblood vessels can be most clearly rendered on a reference image 1displayed at time t1 and an ultrasonic image 2 displayed at time t2, itis determined that they are corresponding images. It can be understoodfrom this that, although the reference image 1 corresponding to theultrasonic image 2 is supposed to be displayed at the position of timet2, the corresponding reference image is displayed at time t1. At thispoint, a difference (the amount of change) between scan-planecoordinates 1 and scan-plane coordinates 2 which are stored in thescan-plane coordinate storing unit 110 corresponds to the amount ofinternal-organ movement. Accordingly, determining the difference betweenthe scan-plane coordinates 1 and the scan-plane coordinates 2 andcorrecting the scan plane coordinates makes it possible to correct acoordinate-system displacement caused by the internal-organ movement.

What is claimed is:
 1. An ultrasonic diagnosis apparatus comprising: adisplay, and an ultrasonic diagnostic system including a processor and amemory, where the ultrasonic diagnostic system operates to: generate anultrasonic image of a scan-plane, from reflection echo signals outputfrom an ultrasonic probe; store volume image data pre-obtained by adiagnostic imaging apparatus, in the memory; detect a three-dimensionalposition of a scan-plane coordinate by a position sensor, in accordancewith a scan-plane coordinate system which is associated in advance witha volume image data coordinate system; extract reference image datacorresponding to the ultrasonic image of the scan-plane from the volumeimage data, in accordance with an association of the scan-planecoordinate system and the volume image data coordinate system, and usethe reference image data to reconstruct a reference image; display theultrasonic image and the reference image on the display, respectively;freeze and maintain the freeze of the reference image responsive to afreeze instruction, to maintain a frozen reference image while change ofthe ultrasonic image is conducted responsive to movement of theultrasonic probe; display the frozen reference image and a changingultrasonic image corresponding to movement of the ultrasonic probe onthe display, while the frozen reference image and the changingultrasonic image are compared with each other; respond to an adjustmentinstruction when the frozen reference image and the changing ultrasonicimage are found to display a same cross section, by determining acoordinate difference between the scan-plane coordinate system and thevolume image data coordinate system, and correcting an associationrelationship between the scan-plane coordinate system of the ultrasonicimage and the volume image data coordinate system in accordance with theadjustment instruction, based on the scan-plane coordinate of theultrasonic probe at the adjustment instruction and the scan-planecoordinate of the ultrasonic probe at the freeze instruction.
 2. Theultrasonic diagnosis apparatus according to claim 1, wherein the volumeimage data is obtained by another diagnostic imaging apparatus.
 3. Theultrasonic diagnosis apparatus according to claim 1, wherein the frozenreference image at the freeze instruction or the changing ultrasonicimage at the adjustment instruction, has a distinctive point of theobject.
 4. The ultrasonic diagnosis apparatus according to claim 1,wherein a correcting device corrects the association relationshipbetween the scan-plane coordinate system of the ultrasonic image and thevolume image data coordinate system of the volume image data, based on adifference between the scan-plane coordinate of the ultrasonic probe atthe adjustment instruction and the scan-plane coordinate of theultrasonic probe at the freeze instruction.
 5. The ultrasonic diagnosisapparatus according to claim 1, wherein the ultrasonic probe is moved todisplay both of the reference image and ultrasound image on the samescan plane, and after the reference image is frozen, the ultrasonicprobe is moved to adjust the changing ultrasound image until displayinga same cross section as the frozen reference image.
 6. The ultrasonicdiagnosis apparatus according to claim 1, wherein the ultrasonic probeis temporarily maintained at a frozen position, the reference image isfrozen as a position indicated by the frozen position of the ultrasonicprobe, and the ultrasonic image is displayed corresponding to theposition indicated by the frozen position of the ultrasonic probe, andthen adjusted by moving the ultrasonic probe from the frozen positionuntil the frozen reference image and the changing ultrasonic image aredisplayed having a same cross section.
 7. An ultrasonic diagnosisapparatus comprising: a display, and an ultrasonic diagnostic systemincluding a processor and memory, where the ultrasonic diagnostic systemoperates to: generate an ultrasonic image of a scan-plane, fromreflection echo signals output from an ultrasonic probe; store volumeimage data pre-obtained by a diagnostic imaging apparatus, in thememory; detect a three-dimensional position of a scan-plane coordinateby a position sensor, in accordance with a scan-plane coordinate system,wherein the scan-plane coordinate system is associated in advance with avolume image data coordinate system; extract reference image datacorresponding to the ultrasonic image of the scan-plane from the volumeimage data, in accordance with an association of the scan-planecoordinate system and the volume image data coordinate system, and usethe reference image data to reconstruct a reference image; display theultrasonic image and the reference image on the display, respectively;freeze and maintain the freeze of the reference image responsive to afreeze instruction, to maintain a frozen reference image while change ofthe ultrasonic image is conducted responsive to movement of theultrasonic probe; display the frozen reference image and a changingultrasonic image corresponding to movement of the ultrasonic probe onthe display, while the frozen reference image and the changingultrasonic image are compared with each other; respond to an adjustmentinstruction when the frozen reference image and the changing ultrasonicimage are found to display a same cross section, by determining acoordinate difference between the scan-plane coordinate system and thevolume image data coordinate system, and correcting a magnification andassociation relationship between the scan-plane coordinate system of theultrasonic image and the volume image data coordinate system inaccordance with the adjustment instruction, based on the scan-planecoordinate of the ultrasonic probe at the adjustment instruction and thescan-plane coordinate of the ultrasonic probe at the freeze instruction.8. The ultrasonic diagnosis apparatus according to claim 7, wherein thevolume image data is obtained by another diagnostic imaging apparatus.9. The ultrasonic diagnosis apparatus according to claim 7, wherein thefrozen reference image at the freeze instruction or the ultrasonic imageat the adjustment instruction, has a distinctive point of the object.10. The ultrasonic diagnosis apparatus according to claim 7, wherein acorrecting device corrects the association relationship between thescan-plane coordinate system of the ultrasonic image and the volumeimage data coordinate system of the volume image data, based on adifference between the scan-plane coordinate of the ultrasonic probe atthe adjustment instruction and the scan-plane coordinate of theultrasonic probe at the freeze instruction.
 11. The ultrasonic diagnosisapparatus according to claim 7, wherein the ultrasonic probe is moved todisplay both of the reference image and ultrasound image on the samescan plane, and after the reference image is frozen, the ultrasonicprobe is moved to adjust the changing ultrasound image until displayinga same cross section as the frozen reference image.
 12. The ultrasonicdiagnosis apparatus according to claim 7, wherein the ultrasonic probeis temporarily maintained at a frozen position, the reference image isfrozen at as a position indicated by the frozen position of theultrasonic probe, and the ultrasonic image is displayed corresponding tothe position indicated by the frozen position of the ultrasonic probe,and then adjusted by moving the ultrasonic probe from the frozenposition until the frozen reference image and the changing ultrasonicimage are displayed having a same cross section.
 13. An ultrasonicdiagnosis apparatus comprising: a display, and an ultrasonic diagnosticsystem including a processor and a memory, where the ultrasonicdiagnostic system operates to: generate an ultrasonic image of ascan-plane, from reflection echo signals output from an ultrasonicprobe; store volume image data pre-obtained by a diagnostic imagingapparatus, in the memory; detect a three-dimensional position of ascan-plane coordinate by a position sensor, in accordance with ascan-plane coordinate system which is associated in advance with avolume image data coordinate system; extract reference image datacorresponding to the ultrasonic image of the scan-plane from the volumeimage data, in accordance with an association of the scan-planecoordinate system and the volume image data coordinate system, and usethe reference image data to reconstruct a reference image; display theultrasonic image and the reference image simultaneously on the display,respectively; and where in the scan-plane coordinate system has lostassociation with the volume image data coordinate system, the ultrasonicdiagnostic system operates differently to: freeze and maintain thefreeze of the reference image responsive to a freeze instruction, tomaintain a frozen reference image while change of the ultrasonic imageis conducted responsive to movement of the ultrasonic probe; display thefrozen reference image and a changing ultrasonic image corresponding tomovement of the ultrasonic probe on the display, while the frozenreference image and the changing ultrasonic image are compared with eachother; respond to an adjustment instruction to reestablish thescan-plane coordinate system association with the volume image datacoordinate system, when the frozen reference image and the changingultrasonic image are found to display a same cross section, bydetermining a coordinate difference between the scan-plane coordinatesystem and the volume image data coordinate system, and correcting anassociation relationship between the scan-plane coordinate system of theultrasonic image and the volume image data coordinate system inaccordance with the adjustment instruction, based on the scan-planecoordinate of the ultrasonic probe at the adjustment instruction and thescan-plane coordinate of the ultrasonic probe at the freeze instruction.14. The ultrasonic diagnosis apparatus according to claim 13, whereinthe volume image data is obtained by another diagnostic imagingapparatus.
 15. The ultrasonic diagnosis apparatus according to claim 13,wherein the frozen reference image at the freeze instruction or thechanging ultrasonic image at the adjustment instruction, has adistinctive point of the object.
 16. The ultrasonic diagnosis apparatusaccording to claim 13, wherein a correcting device corrects theassociation relationship between the scan-plane coordinate system of theultrasonic image and the volume image data coordinate system of thevolume image data, based on a difference between the scan-planecoordinate of the ultrasonic probe at the adjustment instruction and thescan-plane coordinate of the ultrasonic probe at the freeze instruction.17. The ultrasonic diagnosis apparatus according to claim 13, whereinthe ultrasonic probe is moved to display both of the reference image andultrasound image on the same scan plane, and after the reference imageis frozen, the ultrasonic probe is moved to adjust the changingultrasound image until displaying a same cross section as the frozenreference image.
 18. The ultrasonic diagnosis apparatus according toclaim 13, wherein the ultrasonic probe is temporarily maintained at afrozen position, the reference image is frozen as a position indicatedby the frozen position of the ultrasonic probe, and the ultrasonic imageis displayed corresponding to the position indicated by the frozenposition of the ultrasonic probe, and then adjusted by moving theultrasonic probe from the frozen position until the frozen referenceimage and the changing ultrasonic image are displayed having a samecross section.